In the field of accelerometers, it is known to form a small compact accelerometer by etching the relevant parts out of silicon. U.S. Pat. No. 4,574,327 illustrates one version of such a transducer in which a proof mass having a textured surface containing many grooves and apertures extending through the proof mass has its surface tailored in order to achieve the desired frequency response by using the squeeze-film damping phenomenon. In that apparatus, response is hindered by the fact that the surface of the proof mass is corrugated and is not uniform so that the capacitance is much less than it would be if the surface were smooth. Further, the removal of a substantial portion of mass limits the amount of mass available and thereby decreases the sensitivity of the accelerometer.
It is known in the art to form a closed-loop accelerometer, in which the proof mass is electrically urged to a reference position and the voltage or current required for restoration is a measure of the acceleration. One such closed-loop system is shown in U. S. Pat. No. 4,649,748.
Closed-loop micromachined accelerometers in the art have soft springs or hinges because, when the proof mass is in the nominal position, the springs do not exert any force.
The problems evidenced by such prior art devices are the difficulty of tailoring the parameters of the device to accommodate different ranges of acceleration to be measured and the different ranges of frequency response of the device. In a typical design, the mechanical, damping and electrical parameters are interrelated so that changing one parameter will have an adverse affect on others.